1. Field of the Invention
This invention relates to a condensate or mixed bed polishing process and, in particular, to a condensate polishing process which utilizes an inert resin to improve both the separation of anion exchange resins from cation exchange resins in a mixed resin bed and chemical regeneration of the anion and cation exchange resins.
2. Description of the Prior Art
In a steam turbine power plant system it is important to provide water for steam generation which has been treated, i.e. substantially freed of unwanted solid content. Condensate polishing processes are employed to treat the water. In conventional processes, untreated water is passed through a service vessel having a mixed resin bed of anion and cation exchange resins which resins act to remove solid content. Periodically, the mixed resin bed becomes exhausted or "spent", requiring regeneration of the resins. Experience has shown that the most efficient procedure for regeneration is to separate the anion from the cation exchange resins, and then, chemically regenerate the anion exchange resins with caustic regenerant and the cation exchange resins with an acid. Backwashing, which is conventionally employed to separate the mixed resin bed, causes a substantial amount of the higher density cation exchange resins to separate out into a layer in the bottom of the service vessel, while a substantial amount of the relatively lighter density anion exchange resins settle into a layer above the layer of cation exchange resins. However, separation is not complete in that some anion exchange resins settle in the cation exchange resin layer, and conversely, some cation exchange resins settle in the anion exchange resin layer. Furthermore, demarcation between the anion and cation exchange resin layers is difficult, if not impossible, to visualize, and more importantly, the area of demarcation is, in reality, a third layer comprised of anion exchange resins with a small, but appreciable, number of entrained cation exchange resins. Accordingly, the more recent prior art references have been directed to processes wherein regeneration of one resin layer does not result in leakage into the other resin layer, while at the same time resins in the demarcation area can be regenerated and reused to reduce the amount of discarded exhausted resin.